Physical layer frame format design for wideband wireless communications systems

ABSTRACT

Systems and methods are provided for processing a payload portion of a received signal in a single carrier mode or a multiple carrier mode based on a portion of the received signal. A single carrier signaling portion is received at a first rate, and whether the payload portion of the signal is a single carrier signal or a multiple carrier signal is detected from the received single carrier signaling portion. The payload portion of the received signal is received at the first rate and demodulated in a single carrier mode if the detecting determines that the payload portion of the received signal is a single carrier signal, and the payload portion of the received signal is demodulated in a multiple carrier mode if the detecting determines that the payload portion of the received signal is a multiple carrier signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/847,649, filed on Mar. 20, 2013, which is a continuation of U.S.application Ser. No. 12/489,865 (now U.S. Pat. No. 8,441,968), filed onJun. 23, 2009, which is a continuation-in-part of U.S. application Ser.No. 12/410,883 (now U.S. Pat. No. 8,358,668), filed on Mar. 25, 2009,and which also claimed priority from U.S. Provisional Application No.61/078,952, filed on Jul. 8, 2008, the entirety of which is incorporatedherein by reference. U.S. Provisional Application No. 61/043,384, filedon Apr. 8, 2008, U.S. Provisional Application No. 61/044,816, filed Apr.14, 2008, and U.S. Provisional Application No. 61/076,453, filed Jun.27, 2008, are also related and are incorporated herein by reference.

FIELD

The technology described in this patent document relates generally towideband wireless communications, and more particularly to physicallayer frame formats.

BACKGROUND

Continued advances in computer technology increase interest in anddemand for high data rate (e.g., >1 Gbps) wireless communication. Thesehigh data rate communications are often realized through the use of widebandwidths. For example, Gbps data rates are often accomplished usingseveral hundred MHz or several GHz of bandwidth. These large bandwidthsare available around higher carrier frequencies such as the unlicensed60 GHz band. FIG. 1 depicts an example 60 GHz frequency channel plan 30.The 60 GHz frequency channel plan 30 offers four channels 32 of about 2GHz each centered near 60 GHz. While wide bandwidth channels offeropportunities for large data rates, the channels are often vulnerable todelay dispersion (delay spread) even at low range (e.g., less than 10meters).

There are a wide variety of applications that can take advantage ofwireless communications. Two pervasive applications are high data rateat large range applications and low/moderate data rate at short rangeapplications. These applications have their own advantages anddisadvantages.

In a high data rate at large range application, high data rates areachieved, but the system may have to tolerate a high delay spread. Highdelay spreads increase complexity and power requirements in transmittersand receivers. The higher complexity circuitry tends to have largerspace requirements than short range devices, and the higher power needsare more suited for electrical plug-in devices as opposed to batterydevices. In contrast, low/moderate data rate applications at a shortrange may be line-of-sight applications having a short delay dispersionand lower power requirements. These applications may be realized moreeasily in lower complexity handheld portable wireless systems that areoften sensitive to power consumption.

FIGS. 2A and 2B depict block diagrams of a single carrier transmitter 40and a single carrier receiver 50, respectively. In FIG. 2A, an encoder42 receives input data 44 and encodes the data for transmission. Theoutput of the encoder 42 is propagated to a single carrier modulator 46that integrates the encoded data onto a single carrier for transmissionover an antenna 48. In FIG. 2B, the receiver 50 receives single carrierwireless signals via an antenna 52 and propagates the received signalsto a single carrier demodulator 54. The single carrier demodulator 54extracts data from the received single carrier signal and passes theextracted data to a decoder 56. The decoder 56 decodes the extracteddata and makes the decoded data 58 available to downstream circuitry.

FIGS. 3A and 3B depict block diagrams of a multiple carrier transmitter60 and a multiple carrier receiver 70, respectively. In FIG. 3A, anencoder 62 receives input data 64 and encodes the data for transmission.The output of the encoder 62 is propagated to a multiple carriermodulator 66 that integrates the encoded data onto multiple carriers fortransmission over an antenna 68. In FIG. 3B, the receiver 70 receivesmultiple carrier wireless signals via an antenna 72 and propagates thereceived signals to a multiple carrier demodulator 74. The multiplecarrier demodulator 74 extracts data from the received multiple carriersignals and passes the extracted data to a decoder 76. The decoder 76decodes the extracted data and makes the decoded data 78 available todownstream circuitry.

Data modulation schemes tend to be more compatible with someapplications than others. For example, orthogonal frequency-divisionmultiplexing (OFDM) is a multiple carrier multiplexing scheme that issuitable for sustaining high data rates in channels having a large delaydue to the ease of frequency domain channel equalization. This makesOFDM compatible with the high data rate at large range applicationdescribed above, as OFDM offers relatively simple equalization in a highdelay spread channel, supports a longer range, and supports needed highdata rates.

Disadvantages associated with an OFDM scheme, however, include arelatively high hardware complexity and low power efficiencies. In awideband system having a high carrier frequency, such as 60 GHz, poweramplifier (PA) efficiency at the transmitter, and analog-to-digitalconverter (ADC) bit-width at the receiver are engineering designchallenges. Additionally, OFDM introduces high peak-to-average-ratio(PAPR) in the transmitted and received signal waveforms, requiring largeheadroom for the operating point at the power amplifier andanalog-to-digital converter, which may reduce power amplifier efficiencyand increase the complexity of analog-to-digital converter design.

It should be noted that the terms multiple carrier (MC) and OFDMmodulation will be discussed throughout this disclosure and are in mostcases interchangeable. Thus, where OFDM is referenced, other multiplecarrier modulation techniques may be used. Similarly, references tomultiple carrier modulations include OFDM implementations.

FIGS. 4A and 4B depict block diagrams of an OFDM transmitter 80 and anOFDM receiver 90, respectively. In FIG. 4A, an encoder 82 receives inputdata 84 and encodes the data for transmission. The output of the encoder82 is propagated to an OFDM modulator 86 that integrates the encodeddata onto multiple carriers for transmission over an antenna 88. In FIG.4B, the receiver 90 receives OFDM wireless signals via an antenna 92 andpropagates the received signals to an OFDM demodulator 94. The MCdemodulator 94 extracts data from the received OFDM signal and passesthe extracted data to a decoder 96. The decoder 96 decodes the extracteddata and makes the decoded data 98 available to downstream circuitry.

In line of sight channels or other applications requiring lower datarates, a single carrier (SC) modulation with a time-domain equalizer isoften sufficient. A single carrier system may offer simplicity inhardware combined with low power requirements and high transmit powerefficiency. Single carrier modulation may present a constant envelopeand/or low peak-to-average ratio easing power amplifier andanalog-to-digital converter design. However, single carrier systemstypically require complicated equalizers for high delay spread channels,effectively limiting the range for high data rate transfers.

SUMMARY

In accordance with the teachings herein, systems and methods areprovided for a processor-implemented method of processing a receivedsignal including a payload portion and a signaling portion, thesignaling portion of the received signal being a single carrier signal,the payload portion of the received signal being a single carrier signalor a multiple carrier signal. The systems and methods may includereceiving the signaling portion of the received signal at a firstsampling rate and detecting from the signaling portion of the receivedsignal whether the payload portion of the received signal is a singlecarrier signal or a multiple carrier signal. The payload portion of thereceived signal may be received at the first sampling rate anddemodulated in a single carrier mode in response to the payload portionof the received signal being a single carrier signal or a multiplecarrier mode in response to the payload portion of the received signalbeing a multiple carrier signal. Data from the demodulated payloadportion of the received signal may be stored in a computer readablememory.

As another example, a system for transmitting a signal including apayload portion and a signaling portion, where the signaling portion ofthe transmitted signal is a single carrier signal, and the payloadportion of the signal is a single carrier signal or a multiple carriersignal may include a single carrier modulator for modulating at leastthe signaling portion of the transmitted signal and a multiple carriermodulator for modulating the payload portion of the transmitted signalas a multiple carrier signal when the system is in a multiple carriermode. The system may further include a clock for applying a commonsampling rate to an output of the single carrier modulator and an outputof the multiple carrier modulator.

As a further example, a system for processing a received signalincluding a payload portion and a signaling portion, where the signalingportion of the received signal is a single carrier signal, and thepayload portion of the received signal is a single carrier signal or amultiple carrier signal may include a signaling portion analyzerconfigured to receive the signaling portion of the received signal at afirst sampling rate and to detect from the signaling portion of thereceived signal whether the payload portion of the received signal is asingle carrier signal or a multiple carrier signal. The system may alsoinclude a demodulator configured to receive the payload portion of thereceived signal at the first sampling rate and to demodulate the payloadportion of the received signal in a single carrier mode in response tothe payload portion of the received signal being a single carriersignal, where the demodulator is further configured to demodulate thepayload portion of the received signal in a multiple carrier mode inresponse to the payload portion of the received signal being a multiplecarrier signal. The system may further include a computer-readablememory configured to store data from the demodulated payload portion ofthe received signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an example 60 GHz frequency channel plan.

FIGS. 2A and 2B depict block diagrams of a single carrier transmitterand a single carrier receiver.

FIGS. 3A and 3B depict block diagrams of a multiple carrier transmitterand a multiple carrier receiver.

FIGS. 4A and 4B depict block diagrams of an OFDM multiple carriertransmitter and an OFDM multiple carrier receiver.

FIGS. 5A and 5B depict block diagrams of a single carrier transmitterand a dual mode transmitter.

FIGS. 6A and 6B depict block diagrams of a single carrier receiver and amultiple carrier receiver that includes a packet synchronizer/headerdecoder.

FIGS. 7A and 7B depict a dual mode receiver that includes a packetsynchronizer/header decoder and a second dual mode receiver.

FIG. 8 depicts a superframe structure for IEEE 802.15.3c MAC.

FIG. 9 depicts a single carrier modulated packet.

FIG. 10 depicts an OFDM multiple carrier modulated packet.

FIG. 11 depicts an OFDM multiple carrier modulated packet that includesan OFDM channel estimation sequence.

FIG. 12 depicts a common single carrier preamble.

FIG. 13 is a flow diagram depicting detection of a payload transmissionmode based on a carrier cover sequence.

FIG. 14 is a flow diagram depicting detection of a payload transmissionmode based on a carrier spreading sequence.

FIG. 15 depicts a common single carrier header.

FIG. 16 depicts an OFDM multiple carrier modulated packet that includesan OFDM channel estimation sequence and a header tail in the commonsingle carrier header.

FIG. 17 depicts sample timing where the OFDM clock samples at 1.5 timesas fast as a single carrier clock.

FIG. 18 depicts sample timing where the OFDM clock samples at 2 times asfast as a single carrier clock.

FIG. 19 depicts a transmitter configuration for maintaining a coherentspectrum between a single carrier portion and a multiple carrier portionof a received signal.

FIG. 20 depicts an OFDM multiple carrier modulated packet that includesan OFDM channel estimation sequence that does not include a singlecarrier channel estimation sequence.

FIG. 21 depicts an OFDM multiple carrier modulated packet that issampled at the same rate throughout the single carrier and multiplecarrier portions.

FIG. 22 depicts a common preamble portion of an OFDM multiple carrierpacket that is sampled at the same rate throughout the SC and MCportions.

FIG. 23 depicts an OFDM multiple carrier packet that is sampled at thesame rate throughout the SC and MC portions where an OFDM channelestimation sequence is included at the start of the MC portion.

FIG. 24 depicts a single carrier packet that is transmitted at a commonSC/OFDM sampling rate.

FIG. 25 depicts a data packet transmitted at a common SC/OFDM samplingrate having a transmission mode dependent header.

FIG. 26 depicts a dual-mode transmitter configured to transmit a datapacket at a common SC/OFDM sampling rate.

FIGS. 27A and 27B depict a single carrier modulated packet that includesa single carrier header, and an OFDM multiple carrier modulated packetthat includes an OFDM header containing an OFDM channel estimationsequence.

FIG. 28 is a flow diagram for decoding a single carrier mode signal or amultiple carrier mode signal based on a received signaling portion of areceived signal.

FIG. 29 is a flow diagram for a method for transmitting a single carrierpayload or a multiple carrier payload following transmission of a singlecarrier signaling portion of a signal.

FIG. 30 is a flow diagram for a method for transmitting a single carrierpayload or a multiple carrier payload at a common singlecarrier/multiple carrier sampling rate following transmission of asingle carrier signaling portion of a signal.

FIG. 31 illustrates an exemplary implementation of the presentinvention.

DETAILED DESCRIPTION

Based on the application, at least three types of wideband devices maybe present in a wireless network: 1.) SC-Only devices such as simplehandheld, low-range, low-power devices; 2.) MC-Only devices that targetlonger range and higher data rates that are not as sensitive to powerand complexity as SC-Only devices; and 3.) Dual-Mode devices that takeadvantage of both single carrier modulation and multiple carriermodulation that may control or talk with both single carrier andmultiple carrier devices. Co-existence between these various types ofdevices may be problematic, especially if the devices cannot communicateto each other—e.g., SC-Only devices may not be able to communicate withMC-Only devices.

To alleviate these communications issues, a common preamble/header frameformat may be used for the physical layer that may be utilized by allthree types of devices. Using this common format, any device mayunderstand the preamble/header of any packet. This enables networktraffic to be well-controlled without transmission conflicts. Hardwarecomplexity may also be reduced because any device (including the dualmode device) need only implement one single carrier sense,synchronization, header decoding, or channel estimation mechanism at itsreceiver. The common preamble and header is included in transmissions ofboth single carrier modulated packets and multiple carrier modulatedpackets. The common preamble and header is transmitted in a singlecarrier mode such that all three of the above described wideband devicesmay interpret the preamble and header, and all devices in the networkare designed such that all devices can understand the single carriercommon preamble and header.

FIGS. 5A and 5B depict block diagrams of a single carrier transmitter100 and a dual mode transmitter 110 for transmitting packets accordingto the above described format The single carrier transmitter 100 of FIG.5A includes an encoder 102 that receives data 104 that encodes the datafor transmission. A single carrier modulator 106 receives the output ofthe encoder 102 and modulates the encoded data onto a single carrier.The modulated signal is then transmitted via an antenna 108. The singlecarrier transmitter 100 of FIG. 5A is able to send SC packets accordingto the common preamble/header frame format utilizing the same hardwareas the SC-Only transmitter described with reference to FIG. 2A. Thesingle carrier transmitter 100 transmits the common preamble/header viathe antenna 108 and follows the common preamble/header with a singlecarrier payload containing the encoded data.

FIG. 5B depicts a dual-mode transmitter 110 for transmitting packetsaccording to the above described format. The dual-mode transmitter 110is capable of transmitting both single carrier signals and multiplecarrier signals, such as OFDM modulated signals, according to the commonpreamble/header format. The dual-mode transmitter 110 includes anencoder 112 that receives and encodes data 114 for transmission. In boththe single carrier mode and multiple carrier mode, the commonpreamble/header is modulated utilizing a single carrier modulator 116and transmitted via the antenna 118. In a single carrier mode, encodedpayload data from the encoder 112 is modulated using the single carriermodulator 116 and transmitted via the antenna 118 following transmissionof the common preamble/header. In a multiple carrier mode, the commonpreamble/header is modulated by the single carrier modulator 116 andtransmitted via the antenna 118 in a similar fashion as in the singlecarrier mode. However, in the multiple carrier mode, the encoded payloaddata is modulated by the multiple carrier modulator 120 and transmittedvia the antenna 118 following transmission of the single carrier commonpreamble/header.

FIGS. 6A and 6B respectively depict block diagrams of a single carrierreceiver 130 and a multiple carrier receiver 140 that includes a packetsynchronizer/header decoder. Both of the depicted receivers are capableof understanding the single carrier common preamble/header. The receiver130 of FIG. 6A is an SC-Only receiver similar to the receiver describedwith reference to FIG. 2B. The SC-Only receiver 130 receives the singlecarrier common preamble/header via an antenna 132 which propagates thecommon preamble/header to a single carrier demodulator 134 whichprocesses the common preamble/header. The common preamble/headeridentifies whether the following payload portion of the packet is asingle carrier signal or multiple carrier signal. If the commonpreamble/header identifies a single carrier payload, the single carrierdemodulator 134 receives the payload via the antenna 132, demodulatesthe payload, and passes the demodulated payload to the decoder 136,which decodes the data 138 and makes it available to downstreamcircuitry. If the common preamble/header identifies a multiple carrierpayload, the payload is ignored because the single carrier receiver 130cannot process the multiple carrier payload.

As shown in FIG. 6A, the SC-only device does not need to implement anadditional processing block to support multiple carrier packets. Anysingle carrier modulated packet is a “pure” single carrier packet thatrequires no additional processing. Multiple carrier packets areconstructed with a single carrier modulated preamble and header, so thesingle carrier device can decode the header and know theduration/destination of the multiple carrier packet.

Referring to FIG. 6B, the MC-Only receiver 140 is configured tounderstand the single carrier common preamble/header. The MC-Onlyreceiver 140 receives the single carrier common preamble/header via anantenna 142. The received single carrier common preamble/header isprocessed by a packet synchronizer/header decoder 144 that detectswhether the payload portion that follows will be a single carrier signalor multiple carrier signal as well as several characteristics of theincoming payload signal. The packet synchronizer/header decoder 144forwards these detected parameters to a multiple carrier demodulator146. If the packet synchronizer/header decoder detects that the incomingpayload portion of the packet is a single carrier signal, the payload isignored as the multiple carrier demodulator 146 is not capable ofprocessing the single carrier payload. However, if the commonpreamble/header identifies a multiple carrier payload, the multiplecarrier demodulator 146 receives the payload via the antenna 142 asshown at 148, demodulates the payload, and passes the demodulatedpayload to the decoder 150, which decodes the data 152 and makes thedata available to downstream circuitry. As shown in FIG. 6B, the MC-onlyreceiver 140 requires only one additional, simple packet synchronizationand header decoding receiver block for extracting all the physical layerinformation for multiple carrier demodulation/decoding.

FIGS. 7A and 7B depict a dual mode receiver 160 that includes a packetsynchronizer/header decoder and a second dual mode receiver 180. Both ofthe depicted receivers are capable of understanding the single carriercommon preamble/header. The dual mode receiver 160 of FIG. 7A receivesthe single carrier common preamble/header via an antenna 162. Thereceived preamble/header is propagated to a single carrier demodulator164 and a packet synchronizer/header decoder 166. Both the singlecarrier demodulator 164 and the packet synchronizer/header decoder 166process the received preamble/header to detect whether the followingpayload will arrive via a single carrier signal or a multiple carriersignal and to determine parameters of the signal and payload. If theincoming payload is a single carrier payload, the single carrierdemodulator 164 extracts the payload from the single carrier signal andpasses the payload to the decoder 172 which makes the decoded data 174available to downstream circuitry. If the incoming payload is a multiplecarrier payload, the packet synchronizer/header decoder 166 forwardsparameters of the incoming signal and payload to the multiple carrierdemodulator 168. The multiple carrier demodulator 168 receives themultiple carrier signal as shown at 176 and extracts the payload fromthe multiple carrier signal. The extracted payload is then propagated tothe decoder 172 which makes decoded data 174 available to downstreamcircuitry.

Referring to FIG. 7B, the dual mode receiver 180 receives the singlecarrier common preamble/header via an antenna 182. The commonpreamble/header is processed by the single carrier demodulator 184 whichdetects whether the incoming payload portion of the packet is a singlecarrier signal or multiple carrier signal. If the incoming payload is asingle carrier signal, the single carrier demodulator 184 extracts thepayload and passes the payload data to a decoder 186 which makes thedecoded data 188 available to downstream circuits. If the incomingpayload is a multiple carrier signal, the single carrier demodulatoralerts the multiple carrier demodulator 190 and passes along parametersof the incoming payload and signal as shown at 192. The multiple carrierdemodulator 190 receives the incoming multiple carrier payload as shownat 194. The multiple carrier demodulator 190 extracts the payload fromthe multiple carrier signal and forwards the payload to the decoder 186that makes the decoded data 188 available to downstream circuitry.

As illustrated above, the MC-Only and dual mode receivers require only asmall amount of additional hardware to handle the modified packetformat. The receivers may require two sets of sampling clocks that comefrom the same source clock. Alternatively, the receiver may sample usingthe multiple carrier higher clock rate all through the packet and applydigital interpolation for the lower clock rate segments. The receiversutilize the preamble information for determining carrier sense,frequency offset, timing reference, AGC/ADC setting, and single carrierchannel impulse estimation (at least for demodulating the header).

Utilizing the above described or similar transmitters and receivers,coexistence between single carrier and multiple carrier hardware may besupported. Even if the modulation format of the incoming packet is notsupported, an SC-Only or MC-Only device may delay its own transmissionsby understanding the preamble/header to avoid collisions. Coexistencemay be guaranteed by transmitting the single carrier commonpreamble/header at a low rate such that all devices in the network canunderstand.

FIG. 8 depicts a superframe structure 200 for IEEE 802.15.3c MAC. Inthis structure 200, the beacon portion 202 and the contention accessperiod portion 204 make up the preamble/header portion 206 that istransmitted using a single carrier signal transmitted at a low commondata rate. This preamble/header portion identifies whether the payloadportion 208 transmitted during the channel time allocation period willbe transmitted via a single carrier signal or multiple carrier signal aswell as parameters of the coming payload and signal such as the physicallayer demodulation/decoding information of the payload portion. Areceiver determines the characteristics of the incoming payload portion208 of the signal and properties of the incoming signal to prepare forreceipt and demodulation of the signal.

FIGS. 9-11 depict example frames that contain common single carrierpreambles/headers. FIG. 9 depicts a single carrier modulated packet 210.The single carrier modulated packet 210 begins with a common singlecarrier preamble 212 followed by a common single carrier header 214. Thesingle carrier preamble/header portions 212, 214 are followed by asingle carrier physical service data unit (PSDU) 216 that may also bereferred to as a single carrier payload portion 216. As illustrated at218, the entire single carrier modulated packet 210 may be sampled atthe receiver by the same single carrier sampling clock.

FIG. 10 depicts an OFDM multiple carrier modulated packet 220 thatincludes a single carrier preamble/header portion. The packet beginswith a common SC preamble 222 and a common single carrier header 224.The common single carrier preamble/header portions 222, 224 may besampled by the single carrier sampling clock as indicated at 226. Thecommon single carrier preamble/header portions 222, 224 are followed byan OFDM PSDU payload portion 228. This multiple carrier payload portion228 may be sampled by a higher rate OFDM sampling clock as indicated at230. This change in sampling rate from the slower single carriersampling clock 226 to the OFDM sampling clock 230 introduces a clockswitch 232 which may be addressed as will be discussed herein below.

FIG. 11 depicts an OFDM multiple carrier modulated packet 240 thatincludes an OFDM channel estimation sequence. The packet begins with acommon single carrier preamble 242 and a common single carrier header244. The common single carrier preamble/header portions 242, 244 may besampled by the single carrier sampling clock as indicated at 246. Thecommon single carrier preamble/header portions 242, 244 are followed byan OFDM payload portion 248. The OFDM payload portion 248 may be sampledby a higher rate OFDM sampling clock as indicated at 250. This change insampling rate from the slower single carrier sampling clock 246 to theOFDM sampling clock 250 introduces a clock switch 252 as was describedwith reference to FIG. 10. The payload portion 248 of the OFDM packet240 includes the PSDU data portion 254 as well as an OFDM channelestimation sequence (CES) portion 256. The CES portion 256 enables anOFDM demodulator to further calibrate for the incoming data portion 254of the packet as will be described further herein below.

As noted with reference to FIGS. 10 and 11, the single carrier andmultiple carrier portions of a packet may be sampled at different ratesto take advantage of benefits and limitations of the differentmodulation schemes. To avoid out-of-band emission and to fulfill thechannel plan (e.g., as shown in the 60 GHz 802.15.3c plan depicted inFIG. 1), single carrier signals may be transmitted with a sampling clockrate (bandwidth) lower than the overall bandwidth of the assignedbandwidth. This is shown in FIG. 1 at 34 where the single carrierbaseband signal is sampled using a clock of 1.728 GHz. Advancedbaseband/analog pulse shape filtering may also be applied on the SCmodulated baseband signal to further reduce out-of-band emissions and tomaintain the spectrum mask defined by the wireless standard.

In contrast, multiple carrier signals, such as OFDM, may be transmittedusing a higher bandwidth and guard subcarriers (null tones) at the edgesof the inband tones to limit out-of-band emission and maintain thespectrum mask. For example, the OFDM baseband signal may be sampledusing a clock rate of 2.592 GHz, which is 1.5 times the single carriersampling rate. In an OFDM signal, pulse shape filtering is easier torealize due to low subcarrier bandwidth and the presence of guardsubcarriers. This pulse shape filtering may be accomplished using timedomain tapering equivalent to frequency domain convolution, or timedomain convolution maybe used.

FIG. 12 depicts a common single carrier preamble portion 260. The commonsingle carrier preamble portion 260 begins with a signaling portion 262followed by a frame delimiter sequence (SFD) 264. A signaling portionmay include a synchronization portion, a channel estimation portion,and/or a header portion. The frame delimiter sequence 264 may befollowed by a single carrier channel estimation sequence 266.

The synchronization subfield 262 contains signals for synchronizing areceiver with an incoming packet. The synchronization subfield 262 maycontain spreading sequences, such as a Golay sequence of length 128,having pi/2 BPSK modulation (or any other modulation that spreads energyequally in real and imaginary parts of the baseband signal) that areconcatenated repeatedly to help achieve synchronization. The signalingportion 262 may additionally or alternatively contain cover sequencesthat are spread using a spreading sequence. Different cover sequencesmay be used for signaling a receiver about various parameters such as apiconet ID or header rate. Different cover sequences may also be used tosignal the receiver as to whether single carrier modulation or multiplecarrier modulation will be applied to the data payload. If this data isincluded in the signaling portion 262, then the receiver may discoverthe single carrier/multiple carrier mode at the very beginning of thepacket, so that the receiver may set receiving physical layerparameters, such as ADC headroom, ADC precision, AGC gain targets,specific for receiving single carrier data or multiple carrier data.Similarly, different spreading sequences may be used to signal thereceiver whether single carrier modulation or multiple carriermodulation will be applied to modulate the data payload (e.g., the useof different or a pair of complementary Golay sequences identifies theformat of the data payload portion). Additionally, carrier sensing,carrier frequency offset, AGC/ADC setting, and timing reference may bedetermined based on the synchronization subfield. Similarly, differentcover sequences in the SFD portion of the preamble or differentspreading sequences in the CES portion of the preamble may be used tosignal the receiver as to whether single carrier modulation or multiplecarrier modulation will be applied to modulate the data payload.

The frame delimiter sequence 264 is a sequence that establishes frametiming such as the Golay sequence using pi/2 BPSK as in the 802.15.3cdraft standard 2.0. The channel estimation sequence 266 is a sequenceknown to the receiver for single carrier and/or multiple carrier channelestimation such as long complementary Golay sequences with pi/2 BPSK asin the 802.15.3c draft standard 2.0.

FIG. 13 is a flow diagram depicting detection of a payload transmissionmode based on a single carrier cover sequence. A dual mode receiverreceives a single carrier signaling portion of a packet as shown at 272.A determination is made at 274 as to whether a single carrier coversequence is present within the signaling portion that identifies thatthe following data payload portion will be a single carrier signal. Ifthe single carrier data payload cover sequence is in the single carriersignaling portion, the yes branch 276 is taken and the payload portionis demodulated and decoded in a single carrier mode as shown at 278. Ifthe single carrier data payload cover sequence is not in the singlecarrier signaling portion, then the incoming data payload will be amultiple carrier signal and the no branch 280 is taken. The payloadportion is then demodulated and decoded in a multiple carrier mode asshown at 282. Alternatively, the presence of different cover sequencesin the SFD portion may be utilized to detect single carrier or multiplecarrier payload portion transmission.

FIG. 14 is a flow diagram depicting detection of a payload transmissionmode based on a carrier spreading sequence. A dual mode receiverreceives a single carrier signaling portion of a packet as shown at 292.A determination is made at 294 as to whether a single carrier spreadingsequence is present within the signaling portion that identifies thatthe following data payload portion will be a single carrier signal. Ifthe single carrier data payload spreading sequence is in the singlecarrier signaling portion, the yes branch 296 is taken and the payloadportion is demodulated and decoded in a single carrier mode as shown at298. If the single carrier data payload spreading sequence is not in thesingle carrier signaling portion, then the incoming data payload will bea multiple carrier signal and the no branch 300 is taken. The payloadportion is then demodulated and decoded in a multiple carrier mode asshown at 302. Alternatively, different spreading sequences in the CESportion may be utilized for signaling single carrier or multiple carrierpayload portion transmission.

FIG. 15 depicts an example common single carrier header 310. The singlecarrier modulated header contains all of the necessary physical layerdemodulation/decoding information, such as packet length, pilotinsertion information, cyclic prefixes, for both single carrier packetsand multiple carrier packets and may contain the MAC layer header. Thereceiver may obtain MAC header information even if the MAC content inthe payload portion is not decodable, due to an unsupported mode,because all receivers are able to interpret the single carrier headerportion. To increase reliability of header decoding, the common singlecarrier header 310 may be transmitted at a low data rate. The headerillustrated in FIG. 15 is in compliance with the 802.15.3c draft 2.0standard.

As noted with reference to FIGS. 10 and 11, a multiple carrier payloadpacket that begins with a single carrier preamble/header portion mayinclude a jump in sampling frequency between the single carrier portionand multiple carrier portion. This jump may require some compensation atthe transmitters and/or receivers to coherently demodulate and decodethe payload portions.

A first compensation that may be required is compensation to maintaincoherence in carrier frequency at the switch. To accomplish coherence inthe carrier frequency, the transmitter uses the same carrier frequencyacross a multiple carrier payload packet's single carrier and multiplecarrier segments. The same source baseband clock is applied across thetwo segments at the transmitter, where a lower sampling rate forgenerating the single carrier portion of the baseband signal may berealized through interpolation.

Another compensation that may be required is compensation to maintaincoherence in carrier phase at the switch. Spectrum mask/out-of-bandtransmissions may be controlled for the single carrier and multiplecarrier segments of a multiple carrier payload packet through the use ofpulse shaping filters. The phase change at the SC/MC switch point maycause a large out-of-band emission if the phase difference between thelast symbol of the single carrier header and the first sample of themultiple carrier payload portion is large.

One solution is to multiply the whole multiple carrier segment by thephasor of the last symbol of the single carrier header or by a phasorwith a phase close to the phase of the header's last symbol. Forexample, if the header is modulated using pi/2 BPSK and the number ofsymbols in the header is a multiple of 4, then the last symbol is +/−j.Thus, compensation may be achieved by multiplying the multiple carriersegment by j if the last symbol is j or by −j if the last symbol is −j.

A second solution is depicted in FIG. 16. FIG. 16 depicts a portion ofan OFDM MC modulated packet 320 that includes an OFDM channel estimationsequence 322 and a header tail 324 in the common single carrier header326. The single carrier header portion 326 includes a tail subfield atthe end of the header (e.g., 4 ones with pi/2 BPSK modulation, so thatthe last symbol is −j). The OFDM MC payload portion 328 of the packet 32then includes a multiple carrier CES symbol 322 at the beginning ofpayload portion (e.g., the OFDM-CES subfield that may be used for OFDMchannel estimation refinement). The out-of-band emissions may beminimized by designating the last symbol of the header tail 324 suchthat it contains a small phase shift to the first OFDM-CES symbol. Thesmall phase shift between the selected final header tail 324 symbol andthe known beginning of the OFDM-CES enables elimination of the spuriousout-of-band emissions caused by larger phase shifts at the boundary.

Another compensation that may need to be implemented for successfultransition from the single carrier to multiple carrier portions of asingle carrier payload packet having a single carrier preamble/header iscompensation to maintain coherence in power at the switch. The singlecarrier and multiple carrier segments may need to be transmitted withthe same power. To compensation for this coherence of power across thesingle carrier segment and multiple carrier segments, the receiver AGCmay be appropriately set based upon parameters determined from thesignaling portion of the common single carrier preamble.

The jump from single carrier sampling to multiple carrier sampling mayalso require compensation to ensure coherence in timing. For example, inthe case of 802.15.3c, OFDM is sampled at 1.5 times the rate of SC. Inother words, the time duration for two clock cycles of the singlecarrier portion is the same time as the duration for 3 clock cycles ofthe OFDM portion. In the example of 802.15.3c, to help ensure asuccessful change from single carrier to OFDM, the time alignment shouldbe guaranteed at each 2 cycle boundary of the single carrier clock.Interpolation may be used for converting the clock rates from the samesource clock.

FIG. 17 depicts sample timing where the OFDM clock 332 samples at 1.5times as fast as a single carrier clock 334. The clocks are aligned suchthat a first pulse 336 of the OFDM clock 332 is aligned with a firstpulse 338 of the single carrier clock 334, and a fourth pulse 340 of theOFDM clock 332 is aligned with a third pulse 342 of the single carrierclock 334 as shown at 344.

FIG. 18 depicts sample timing where the OFDM clock 352 samples at 2times as fast as a single carrier clock 354. In the example of FIG. 18,the OFDM clock 352 begins one single carrier pulse width 356 after thelast single carrier header sample 358 as shown at 360. Alternatively,the OFDM clock could run continuously in a similar fashion as shown inFIG. 17, where a first OFDM pulse would align with a first singlecarrier pulse and a third OFDM pulse would align with a second singlecarrier pulse.

As described above, in a single carrier packet containing a singlecarrier preamble/header portion, the receiver may rely on a CES in thesingle carrier portions as described with reference to FIG. 12, or theMC portion of the packet may contain an SC-CES sub-portion as describedwith respect to FIG. 11. In the case where the receiver uses theinformation of the SC-CES portion to perform both single carrier and MCchannel estimation for both single carrier preamble/header and MCpayload demodulation, a coherent spectrum may be kept across the switchfrom single carrier to multiple carrier.

The SC-CES usually derives a channel impulse response with high accuracydue to the processing gain sampled at the single carrier sampling rate.Using the SC-CES, multiple carrier frequency domain (per-sub-carrier)channel estimation may be obtained by over-sampling the estimatedchannel response to the multiple carrier clock rate and performing afast-Fourier transform (FFT) on the detected samples. The FFT may beapplied directly on the time-domain channel estimate, and the resultantfrequency domain channel estimate may be downsampled (e.g., to 352(336+16) tones). To utilize the SC-CES for multiple carrier channelestimation, the frequency response for single carrier and multiplecarrier may need to be near identical to guarantee the quality of themultiple carrier channel estimate.

An equivalent channel is the combination of the over-the-air channel,analog filters at the transmitter and receiver, and digital (pulseshaping) filters at the transmitter and receiver. The over-the-airchannel and analog filters at the transmitter and receiver are oftencommon between the single carrier and multiple carrier segments.However, the digital filters may be different based on designrequirements of the single carrier and multiple carrier segments.

A first mechanism for maintaining a coherent spectrum across the singlecarrier and multiple carrier portions of a packet is to have the singlecarrier and multiple carrier segments utilize the same digital filter atthe transmitter using the same sampling rate. FIG. 19 depicts atransmitter configuration for maintaining a coherent spectrum between asingle carrier portion and an OFDM or other multiple carrier portion ofa received signal. To accomplish this, both segments 372 may beupsampled to the same rate, as shown at 374, and then the same digitalfilter is applied 376 before entering a digital-to-analog converter(DAC) 378.

A second mechanism is to predetermine and fix digital pulse shapingfilters for the single carrier and multiple carrier segments such thattheir frequency responses (amplitude and phase) on different subcarriersare known by both the transmitter and receiver. While filter amplitudesare often flat over the data subcarriers, this second mechanism maylimit implementation flexibility.

In addition to using the SC-CES to perform channel estimation for themultiple carrier portion of the packet, the multiple carrier portion ofthe packet may contain its own MC-CES. In cases where channel estimationis performed using an MC-CES, compensation to maintain a coherentspectrum as described above is not necessary. In addition, if an MC-CESis utilized and the packet is a multiple carrier payload packet,transmission of the SC-CES may not be necessary. FIG. 20 depicts an OFDMmultiple carrier modulated packet 380 that includes an OFDM channelestimation sequence 382 that does not include a single carrier channelestimation sequence. This is shown at 384 where the common singlecarrier preamble does not contain a CES sub-portion. This can becontrasted with the example common single carrier preamble describedwith reference to FIG. 12 above.

The SC-CES may still need to be applied for packets having a singlecarrier payload. The receiver may be configured to be able to tellwhether a single carrier payload is forthcoming, and thus whether anSC-CES is coming, based on the signaling portion 386 of the commonsingle carrier preamble 384. If the SC-CES is not transmitted, thereceiver may use the signaling portion 386 of the common single carrierpreamble 384 to determine single carrier channel estimation (e.g., byadaptive training as in 802.11b), so that the header can still becorrectly decoded. Because the header may be spread using a highspreading factor, it may be robust against channel estimationinaccuracies that might be caused by removing the SC-CES.

As an additional example, the SC-CES and an MC-CES may be transmitted ina multiple carrier payload packet. A first channel estimate may becalculated for the entire packet based on the SC-CES sub-portion. Asecond channel estimate may also be calculated based on the receivedMC-CES sub-portion of the multiple carrier payload portion. Both ofthese first and second channel estimates may be utilized to generate afinal channel estimate that is used in processing the multiple carrierpayload portion.

FIG. 21 depicts an additional example where an OFDM multiple carrierpacket 390 is sampled at the same rate 392 throughout the SC 394 and MC396 portions. In this example, the SC 394 and MC 396 portions of thepacket utilize the same sampling rate throughout. For example, both theSC 394 and MC 396 portions of the packet may be sampled at about a 2 GHzrate (e.g., 1.95 GHz to 2.05 GHz). Both portions may fulfill thespectrum mask defined by the regulation authority through appropriatedigital and analog filtering. In this case no sampling rate switching isrequired between the SC and OFDM portions. Utilizing a common samplerate for both single and multiple carrier packets improves the ease ofcoexistence, as each device needs only to implement one set ofdemodulation/decoding schemes for receiving the preamble/header. Thenon-appearance of the sampling rate jump between the single carrierportion and OFDM portion of the packet mitigates the need for several ofthe compensations described above. Additionally, if the same digitalfilter is applied throughout the transmitted packet at the transmitter,the SC-CES may be used for channel estimation throughout the entirepacket. Thus, the OFDM-CES may not be needed, further improving physicallayer efficiency. As an alternative, an OFDM-CES may be used without useof an SC-CES. As a further alternative, both an SC-CES and OFDM-CES maybe used to gain reliability.

FIG. 22 depicts a common preamble portion 408 of an OFDM multiplecarrier packet 400 that is sampled at the same rate 402 throughout theSC 404 and MC 406 portions. The common preamble 408 includes a singlecarrier synchronization portion 410 that includes a frame delimitersequence. The common preamble 408 also includes a common (SC/OFDM)channel estimation sequence 412. The SC/OFDM CES 412 is a channelestimation sequence that can be used for the channel estimation ofsingle carrier and/or OFDM signals in the payload and/or the header 414.

FIG. 23 depicts an OFDM multiple carrier packet 420 that is sampled atthe same rate 422 throughout the SC 424 and MC 426 portions where anOFDM channel estimation sequence 427 is included at the start of the MCportion 426. The OFDM CES 427 may not be included in SC payload packets.For example, an SC payload packet may utilize the contents of the SYNCportion 428 of the SC portion for gaining sufficient SC channelestimation. The packet 420 concludes with an OFDM payload portion 429.

FIG. 24 depicts a single carrier packet 430 that is transmitted at acommon SC/OFDM sampling rate 432. The single carrier packet 430 depictedin FIG. 24 is the single carrier modulation version of the nearlyidentical multiple carrier packet of FIG. 22. The single carrier packet430 includes a common preamble 434 that includes a synchronizationportion 436 as well as a common SC/OFDM channel estimation sequence 438.The single carrier packet 430 further includes a common header 440 andan SC payload 442.

FIG. 25 depicts a data packet 450 transmitted at a common SC/OFDMsampling rate 452 having a transmission mode dependent header 454. Thepacket 450 includes a common SC preamble 456 that contains asynchronization portion 458 and a common SC/OFDM channel estimationsequence 460. After the common preamble 456, a transmission modedependent header 454 is transmitted. The header 454 is either an SCheader or an OFDM modulated header based on the payload 462 modulationformat (i.e., SC payload goes with SC header; OFDM payload goes withOFDM header).

FIG. 26 depicts a dual-mode transmitter 470 configured to transmit adata packet at a common SC/OFDM sampling rate. The transmitter 470includes a single carrier modulator 472 for modulating single carrierportions of a data packet including at least a common preamble as wellas a single carrier payload when the transmitter 470 is in a singlecarrier packet mode. An output of the single carrier modulator 472 issampled according to an output of a common clock 474. The transmitteralso includes a multiple carrier modulator 476 for modulating multiplecarrier portions of a data packet that include a multiple carrierpayload when the transmitter 470 is in a multiple carrier packet mode.An output of the multiple carrier modulator 476 is also sampledaccording to an output of the common clock 474 such that signals fromthe single carrier modulator 472 and the multiple carrier modulator 476are sampled at the same data rate (e.g., ˜2 GHz). A multiplexer 478selects from between the sampled single carrier modulator 474 output andthe sampled multiple carrier modulator 476 output (e.g., at thetransition between a single carrier common preamble/header and multiplecarrier payload). The selected signal is processed at a digital toanalog converter 480 and transmitted wirelessly via an antenna 482.

FIGS. 27A and 27B depict a further example. FIG. 27A depicts a singlecarrier modulated packet 500 that includes a single carrier header. FIG.27B depicts an OFDM multiple carrier modulated packet 506 that includesan OFDM header that contains an OFDM channel estimation sequence. Asshown in FIG. 27A, the single carrier payload packet 500 includes acommon single carrier preamble segment 502 and a single carrier headerportion 504. In this example, a single carrier payload packet is of asimilar form as described above. A variation is shown, however, in themultiple carrier payload packet 506 shown in FIG. 27B. The OFDM multiplecarrier modulated packet 506 of FIG. 27B contains a common singlecarrier preamble portion 508 similar to the one shown in FIG. 27A.However, the OFDM payload packet of FIG. 27B does not include a headerportion of the packet in the single carrier portion of the frame.Instead, the clock switching occurs immediately following the singlecarrier preamble portion 508, as illustrated at 510. An OFDM-CESsub-portion is transmitted followed by an OFDM header portion 512, whichis transmitted during the OFDM portion of the OFDM payload packet 506.The OFDM header 512 is then followed by the OFDM payload portion.

FIG. 28 is a flow diagram for decoding a single carrier mode signal or amultiple carrier mode signal based on a received signaling portion of areceived signal. A single carrier signaling portion of the receivedsignal is received as shown at 522. From the received signaling portion,whether the payload portion of the received signal will be a singlecarrier signal or a multiple carrier signal is detected at 524. If asingle carrier payload is signaled by the signaling portion, then thepayload portion of the signal is demodulated and decoded in a singlecarrier mode as shown at 526. In contrast, if a multiple carrier payloadis signaled by the received signaling portion, then the payload portionis demodulated and decoded in a multiple carrier mode as shown at 528.At 530, the decoded payload is then stored in a computer readablememory.

FIG. 29 is a flow diagram for a method for transmitting a single carrierpayload or a multiple carrier payload following transmission of a singlecarrier signaling portion of a signal. At 542, a determination is madewhether to send a payload portion of a signal in a single carrier modeor a multiple carrier mode. The transmitter transmits an appropriatesingle carrier signaling portion of the signal as shown at 544. Thesignaling portion may identify whether the following payload portion isa single carrier or multiple carrier payload. If the determination ismade to send a multiple carrier payload, then the payload is transmittedover multiple carriers as shown at 546. In contrast, if a single carrierpayload is to be sent, then the payload is transmitted over a singlecarrier as illustrated at 548.

FIG. 30 is a flow diagram for a method for transmitting a single carrierpayload or a multiple carrier payload at a common singlecarrier/multiple carrier sampling rate following transmission of asingle carrier signaling portion of a signal at a first sampling rate. Asingle carrier signaling portion of the received signal is received at afirst rate as shown at 562. From the received signaling portion, whetherthe payload portion of the received signal will be a single carriersignal or a multiple carrier signal is detected at 564. At 566, apayload portion of the received signal is received at the first samplingrate. If a single carrier payload is signaled by the signaling portion,then the payload portion of the signal is demodulated and decoded in asingle carrier mode as shown at 568. In contrast, if a multiple carrierpayload is signaled by the received signaling portion, then the payloadportion is demodulated and decoded in a multiple carrier mode as shownat 570. At 572, the decoded payload is then stored in a computerreadable memory.

The above described concepts may be implemented in a wide variety ofapplications including those examples described herein below. Referringto FIG. 31, the present invention may be embodied in a device 580. Thedevice can be a device that receives wireless signals—e.g., a storagedevice, a computer system, a smart phone, a set top box, a cellularphone, a personal digital assistant (PDA), a vehicle, and so on. Thepresent invention may implemented within signal processing and/orcontrol circuits, which are generally identified in FIG. 31 at 584, aWLAN interface and/or mass data storage of the device 580. In oneimplementation, the device 580 receives signals from a source andoutputs signals suitable for a display 588 such as a television and/ormonitor and/or other video and/or audio output devices. Signalprocessing and/or control circuits 584 and/or other circuits (not shown)of the device 580 may process data, perform coding and/or encryption,perform calculations, format data and/or perform any other function asrequired by a particular application.

The device 580 may communicate with mass data storage 590 that storesdata in a nonvolatile manner. Mass data storage 590 may comprise opticaland/or magnetic storage devices for example hard disk drives HDD and/orDVDs. The device 580 may be connected to memory 594 such as RAM, ROM,low latency nonvolatile memory such as flash memory and/or othersuitable electronic data storage. The device 580 also may supportconnections with a WLAN via a WLAN network interface 596.

This written description uses examples to disclose the invention,including the best mode, and also to enable a person skilled in the artto make and use the invention. It should be noted that the systems andmethods described herein may be equally applicable to other frequencymodulation encoding schemes. The patentable scope of the invention mayinclude other examples that occur to those skilled in the art.

It is claimed:
 1. A receiver comprising: an antenna configured toreceive a data packet that includes (i) a signaling portion that issingle carrier modulated and (ii) a payload portion that is multiplecarrier modulated; a single carrier demodulator configured to demodulatethe signaling portion using a single carrier scheme; and a multiplecarrier demodulator configured to demodulate the payload portion using amultiple carrier scheme; wherein the single carrier demodulation schemeand the multiple carrier demodulation scheme are configured to use thesame sampling rate.
 2. The receiver of claim 1, wherein the receiver isconfigured to align sampling times between the single carrier scheme andthe multiple carrier scheme.
 3. The receiver of claim 1, wherein thesingle carrier demodulator is configured to demodulate a single carriermodulated channel estimation sequence (CES) of the packet using thesingle carrier scheme to yield a first demodulated CES, and wherein themultiple carrier demodulator is configured to demodulate a multiplecarrier modulated CES of the packet using the multiple carrier scheme toyield a second demodulated CES.
 4. The receiver of claim 3, furthercomprising a processor configured to: calculate, based on the firstdemodulated CES, a first channel estimate that is applicable to allportions of the packet; and calculate, based on the second demodulatedCES, a second channel estimate that is applicable to only the payloadportion.
 5. The receiver of claim 4, wherein the processor is configuredto generate, from the first channel estimate and the second channelestimate, a final channel estimate to be used in processing the payloadportion.
 6. The receiver of claim 1, wherein the multiple carrier schemeis based on orthogonal frequency-division multiplexing (OFDM).
 7. Aprocessor-implemented method comprising; receiving a data packet thatincludes (i) a signaling portion that is single carrier modulated and(ii) a payload portion that is multiple carrier modulated; demodulatingthe signaling portion using a single carrier scheme; and demodulatingthe payload portion using a multiple carrier scheme; wherein the singlecarrier demodulation scheme and the multiple carrier demodulation schemeuse the same sampling rate.
 8. The method of claim 7, furthercomprising: aligning sampling times between the single carrier schemeand the multiple carrier scheme.
 9. The method of claim 7, furthercomprising: demodulating a single carrier modulated channel estimationsequence (CES) of the packet using the single carrier scheme to yield afirst demodulated CES; and demodulating a multiple carrier modulated CESof the packet using the multiple carrier scheme to yield a seconddemodulated CES.
 10. The method of claim 9, further comprising:calculating, based on the first demodulated CES, a first channelestimate that is applicable to all portions of the packet; andcalculating, based on the second demodulated CES, a second channelestimate that is applicable to only the payload portion.
 11. The methodof claim 10, further comprising: generating, from the first channelestimate and the second channel estimate, a final channel estimate to beused in processing the payload portion.
 12. The method of claim 7,wherein the multiple carrier scheme is based on orthogonalfrequency-division multiplexing (OFDM).